Breath analyzers such as the portable breath testers used by police for the screening of drivers suspected of driving while under the influence of alcohol require the delivery of a sustained breath sample by the person being tested. Delivery of a proper sample requires the tested person or user to breathe into a sampling head connected to the tester. The sampling head is fitted with a mouthpiece against which the mouth of the user is placed. Such testers are described for example in U.S. Pat. No. 3,764,270 issued to Collier et al. Because the use of conventional breath testers usually occurs under the supervision of a police officer or is voluntary, there is little danger that the sample of gas which is tested will be other than an authentic sample of the breath of the specified person. There are other applications of portable breath analyzers, however, where the authenticity of the breath sample cannot be so easily assured.
For example, sometimes a breath alcohol test is performed by a test subject without human supervision. Where the test subject fears failing the test, he or she may resort to various techniques aimed at circumventing the test (i.e., cheating) including attempts to provide a bogus sample to the test apparatus instead of his or her own breath. An example of an application in which this is a problem is the breath analyzer incorporated into an ignition interlock system of an automobile or other equipment. Such a system is described in U.S. Pat. No. 4,093,945 issued to Collier et al. expressly incorporated herein by reference in its entirety. Sobriety interlock systems, as they are commonly referred to, link an alcohol breath tester to the ignition system of machinery such as an automobile. They operate by requiring a test subject to satisfy one or more preconditions including passing a breath alcohol test before enabling the vehicle or other equipment to be started. Conscientious drivers may install vehicle interlocks in their automobiles as a safety measure and use them voluntarily. On the other hand, the use of an interlock is frequently compelled to some degree. For example, a teen who borrows a family vehicle equipped with an interlock may not be a truly voluntary user. The same may be true of some employees in cases where an employer seeks liability protection by installing interlocks on company vehicles. Moreover, the installation of a vehicle interlock is increasingly dictated by court order as a condition for allowing persons convicted of driving under the influence of alcohol to continue to drive so they can maintain their employment and/or obtain counselling.
Another case where breath testing may be performed without direct supervision and where attempts at circumvention may be a problem is in the "home arrest" or remote confinement systems to which local governments are increasingly turning as a way to relieve the problem of overcrowding in prisons. In such a system, an offender is sentenced to be confined at a location such as the offenders' home. The presence and the sobriety of the offender can be remotely monitored electronically. To protect the safety of both the offender and the public to the fullest extent possible, reasonable assurance must be provided that others will not be able to substitute themselves for the offender in the alcohol breath test procedure in order to pass the test in place of the offender.
In the use of a vehicle interlock system, or a remote confinement system which monitors a confinees' use of alcohol, or other system in which there is no manual supervision of the performance of a breath test by the person using the system, the opportunity exists for the test subject to attempt to circumvent the test by providing a bogus sample to the tester in lieu of a contemporaneous breath sample. Such circumvention may be attempted by delivery of alcohol-free gas samples from balloons or hoses attached to the mouthpiece of the tester. If successful, the test apparatus may analyze the bogus gas as it would an authentic breath sample and enable the starting of the engine or the signalling of the passage of a sobriety test. Subjects may also attempt to circumvent the interlock by passing the breath sampling mouthpiece to an accomplice who has not been drinking in excess. The accomplice cooperates with the intended subject by providing a substitute breath sample.
When breath alcohol measurements are used as the basis of unsupervised sobriety testing, it is, particularly for a vehicle interlock or home arrest system, desirable that the system include one or more anti-circumvention means capable of reasonably ensuring a correct test result without human supervision.
An unsupervised sobriety testing system ought to be capable of discriminating between a contemporaneous breath sample and substitute gases such as air from bicycle pump or a filling station air hose, bellows or previously inflated balloon. Illustrations of systems aimed at achieving the foregoing are discussed in U.S. Pat. Nos. 4,592,443, 3,831,707, and 3,824,537. U.S. Pat. No. 4,592,443 proposes measuring the temperature of the gas and determining whether it falls within a range expected for breath. Breath being moist, U.S. Pat. No. 3,831,707 proposes sensing humidity in the gas to avoid circumventing the system with a bogus gas that is drier than breath. U.S. Pat. No. 3,824,537 teaches requiring the operator to place one hand on a button which must be activated during a test period while the other hand is used to hold a breath sampling tube located some distance away from the button. Since the hands of the operator must be placed some distance apart, deceptive manipulation of a bellows or the like is discouraged.
Secondly, an unsupervised sobriety testing system ought to ensure that the alcohol measurement is performed on a sample of alveolar gas, commonly referred to in the art as a "deep lung sample". As used herein and in the claims that term refers to a breath sample consisting of a proportion of alveolar gas sufficient to permit an accurate determination of blood alcohol level. Since breath expired from upper portions of the respiratory tract does not necessarily have an alcohol level proportional to that of the bloodstream, a deep lung sample is essential if the system is not to be defeated by shallow exhalations or a series of short puffs of breath expelled from upper portions of the respiratory tract. This problem is addressed effectively in U.S. Pat. Nos. 4,093,945 and 3,764,270 issued to Collier et al. The Collier et al. patents disclose means, preferably flow sensing means such as a pressure switch combined with timer system, to ensure an essentially continuous and uninterrupted flow of breath sufficient in volume to yield a deep lung sample.
A third important requirement in an unsupervised sobriety testing system is the need for effectively deterring a person other than a designated user, such as the prospective vehicle operator or a specified remotely confined prisoner in a home arrest program, from taking the breath test in place of that operator in order to start the vehicle or pass a confinement condition test. Confirmation of the identity of the operator is particularly important in sobriety testing in situations where performance of the sobriety test by the user is not entirely voluntary.
A vehicle interlock system which is specially adapted to permit unsupervised confirmation of the identity of a designated user is described in detail in commonly assigned U.S. Pat. No. 4,738,333, which is expressly incorporated herein by reference in its entirety. In that system, a designated test subject is trained to perform an identity-confirming act which is not readily learnable in fewer than a given number of attempts at performing the act. In one preferred embodiment, this act comprises blowing a sequence of breath pulses into the mouthpiece of the interlock according to predetermined timing requirements. The system monitors the attempts of a user to perform the identity confirming act and will not allow the vehicle to be started unless the act is correctly performed in fewer than the given number of attempts regardless of the outcome of any breath alcohol test. The system preferably also requires that at least a portion of the identity-confirming act take place substantially contemporaneously with at least a portion of the delivery of the breath sample to be measured. This helps to avoid circumvention of the test by such methods as having the designated, trained subject perform the identity-confirming act but having an accomplice who has not been drinking in excess deliver a substitute breath sample. Requiring performance of the identity-confirming act within a given number of attempts and temporally overlapping the act with delivery of the breath sample where the act itself requires blowing breath into the same mouthpiece into which the breath sample to be tested is delivered provides substantial assurance that the trained test subject rather than some individual is the person who delivered the breath sample. This system represents a major advance in the art and has proven itself to be highly effective. Nevertheless, enhanced security is seldom a matter of absolutes but rather, a question of decreasing the chances that a circumvention attempt will be successful.
While the above system provides greatly increased assurance that the individual who delivers a gas sample into the system for testing is in fact the designated, trained subject rather than an accomplice, there is still some chance that the trained subject could circumvent the system by using some bogus gas delivery device. For example, since the designated subject knows by virtue of his or her previous training the required timing parameters according to which the associated with the identity-confirming act, that person could attempt to simulate a required sequence of breath pulses with some other gas delivered into the mouthpiece of the system from a balloon, compressed gas bottle or other positive pressure gas supply. By modulating the flow of gas from the bogus supply, the subject might acceptably duplicate the required flow parameters. In the case of a balloon, this might be done by properly pinching closed and letting open the neck of a balloon whose mouth enveloped the inlet of the system mouthpiece. More elaborate schemes involving valve arrangements might also be employed in attempt to circumvent the system.